Well according to the Wikipedia file information page (link) the photo was taken on 14th December 2007 and was uploaded by a user called Nandesuka. Not much info is known, it may not even be his dick but he was the person who uploaded it.

Well, we don't know whose cock it is. The U.S. has the world's most famous unknown soldier memorial, and we have no idea who is in it, by definition (one unknown soldier from each war, if I remember correctly).